Ethernet has emerged as the standard of choice for local area networks (LAN). With speeds of 10 Mbps, 100 Mbps, 1 Gbps and soon 10 Gbps, Ethernet capacity has grown to meet the need for increased network capacities. Consequently, there is considerable interest by operators of metropolitan and backbone networks in offering Ethernet based virtual private network services to enterprises to extend their local area Ethernets over the wide area.
A Virtual Private LAN Segment (VPLS) is a type of virtual private network in which the packets steered to a destination between VPN sites are Ethernet packets. VPLS service is also known as transparent LAN service (TLS).
At the same time operators of public data networks can gain capital and operating benefits by consolidating all of the services they offer onto one type of network core. Increasingly that core network is planned to be an MPLS network. To offer a VPLS service to multiple customers involves transporting the customers' Ethernet packets over an MPLS core network.
Despite the inherent elegance of this conceptual network, actual implementation of such networks must devise physical and/or logical arrangements to insure optimal performance, scalability, and operability. One approach to the scaling challenges is to distribute the VPLS service mechanisms over two sorts of platform such as is proposed in the Logical Provider Edge. Herein these two platforms are called the Edge-PE and the Core-PE.
One such distributed functionality approach is Kompella's DTLS solution proposed in an Internet draft. However this solution requires a network wide numbering of VPN sites. This proposal therefore has an administrative burden of having to insure a unique VPN site ID for each instance of each VPN. This may require network administrators to put a limit on the number of sites that can participate in the VPN.
Scaling is another issue associated with Kompella's proposal. In DTLS only one MPLS label space can be used for identifying the tunnels between all Edge-PE of each VPLS.
Another distributed functionality approach for VPLS service realization is a proposal known as Hierarchical VPLS. It has the shortcoming of a requirement for the Core-PE to learn all of the customer MAC addresses of all of the VPN that its subtending Edge-PE server. In large-scale deployments, this may prove to be too many MAC addresses for a Core-PE to learn.